Junpei has dark buzzcut hair, grayish eyes, and a goatee. He is shown to be taller than both the male and female protagonist, yet slightly shorter than Akihiko. He is often seen with both of his hands on his belt, except while wielding a two-handed sword.

While at school and in Tartarus he is in the school uniform of Gekkoukan High, along with a purple collared shirt, a baseball cap, a silver necklace, and a chain attached to his pants. On weekends off, he wears a black leather jacket with a white shirt, black pants, his hat, and necklace. On summer days off, he wears a faded black tank top and navy blue jeans. He never seems to be without with his hat except in two anime scenes (Group Picture and Resolve), or his necklace, which is not worn while in Yakushima for summer vacation, Kyoto while on free time, or in the hot springs.

In Persona 4 Arena Ultimax he is now 19 years old. His hair is now slightly grown out, and wears his hat backwards. He reappears wearing an aqua baseball player uniform with a black tank top and white gloves.

Junpei is portrayed as somewhat goofy, perverted, kind, caring, upbeat, and sometimes serious in missions and other events. After school, he is seen reading manga or playing video games.

He becomes jealous of the protagonist's special power (regardless of gender), and this often results in outbursts aimed at the protagonist out of frustration (his jealousy over the protagonist's abilities were especially pronounced in Spring of Birth). This is partly because he wants to be a leader.

Other times, he is shown to be depressed or angry as a result of his father's alcoholism. Besides these displays of negativity, however, Junpei's attitude usually remains carefree and light-hearted, and when spoken to he often cracks jokes.

His personality undergoes a change once he meets Chidori and gets to know her, showing a more caring side to him than what he usually shows to others (although a friendly side becomes apparent in the female protagonist route, it does not develop as far as Junpei's relationship with Chidori). However, Chidori's sudden reluctance to see him anymore startles him, and he falls into a depressed state. Towards the end of November, Chidori attempts to attack Junpei, and throwing him into distress. This same night, Takaya shoots Junpei in the stomach, killing him. His death and subsequent revival by Chidori, an act which caused her own death, sent Junpei back into a depressed state. Only with the discovery of Chidori's sketchbook and the pictures of him that she drew did he find the strength bounce back, resolving to be a better friend to all those close to him.

In The Answer, he decides to leave the past as it is, contrary to Yukari's feelings.

Junpei Iori is one of the protagonist's friends. Junpei feels insecure and often hides this with humor and boasting. His insecurities lead to jealousy, toward the protagonist. Junpei fights with a two-handed sword, but wields it more like a bat due to his lack of combat training. Like most of the playable characters, Junpei is a student at Gekkoukan High School, and has been in Yukari's class before.

Akihiko Sanada found him during the Dark Hour, crying and disoriented in a convenience store. As soon as Junpei discovers he has the ability to summon a Persona, he joins SEES and moves into the dorm, an action which irritates Yukari Takeba. Junpei is glad to join the team, as it gets him away from his alcoholic father, whom he resents.

Junpei fancies himself as a ladies man, and has a somewhat dirty mind. He makes quick and inaccurate assumptions about the protagonist and Yukari's relationship, when she mentions 'last night'. Junpei is usually the first to comment on how attractive the ladies of SEES are. On vacations, he attempts to pick up the local women, usually dragging his guy friends along.

Junpei is eager to fight, because playing hero makes him feel important. He commonly neglects his school work and uses SEES to boost his low-self esteem. Junpei grows jealous of the protagonist, due to his Wild Card ability and position as the field leader of SEES. Junpei acts recklessly, often attempting to prove himself to his teammates. Junpei ends up falling for Chidori Yoshino, a member of Strega.

Junpei resolved by Chidori's death.

Chidori's loyalty to Takaya Sakaki and Junpei's position with SEES ends up conflicting, resulting in Junpei being fatally shot by Takaya. Chidori sacrifices herself and uses her Persona to restore Junpei to life. He becomes more focused due to her death, and his Persona, fusing with Chidori's Persona Medea, becomes Trismegistus. Chidori's residual power remains with Junpei, allowing him to regenerate health over time.

In the updated version of Persona 3, if the protagonist encourages Junpei to go see Chidori after she tells him that she does not want to see him again, then Chidori will be later seen back in the hospital, alive but with little memory, only recalling someone in her dreams, which is presumed to be Junpei. Junpei, along with Yukari and Fuuka, cry in happiness to see such a thing. According to the doctor that looked after her, her mysterious revival is likely to due to the flowers he placed on her as a sort of memorial. Apparently, whenever the flowers threatened to wilt, Chidori would revive them using her own life. Its theorized by the doctor that the flowers may have given Chidori back her life due to the numerous times she had revived them.

When Junpei becomes trapped in the dorm, he and Koromaru form an independent party to search for supplies in the Abyss of Time. Aigis ends up discovering a supply route before Junpei, which causes his party to disband. Junpei then becomes playable again. Unlike Yukari, Junpei isn't bothered by the thought of returning to fight the Shadows.

When the player opens the door leading to the flashback about Junpei's past, the player sees him taking a stroll at Pawlownia Mall to forget about his depressing coexistence with his alcoholic father. There he, by chance, meets Koromaru and gets along easily with him. Two school partners then appear and invite Junpei to have some drinks at the Escapade Club, but he rejects their proposal since he's not still the legal age to drink and, besides, he wasn't in the mood because of his father. After the flashback he tells Aigis that his father has slightly overcome his addiction, but he still drinks a fair amount of alcohol.

Before the battles between the SEES members, Junpei acts as the rational voice of the team, he tries to calm everyone down and try and solve the problem without the need for battle. When this fails, he forms a team with Koromaru to battle Aigis and Metis for the keys. When the pair are defeated by Aigis, they become two of the torches that surround the arena, along with Akihiko and Ken, and is later followed by Yukari and Mitsuru.

After the True key is forged, Junpei and the rest of SEES decide to open the door that leads to the past Paulownia Mall, where they find a giant door that leads to the moment in time when the protagonist sealed Nyx and they encounter Erebus.

Junpei represents the Magician Arcana Social Link for the female protagonist route. Junpei can only be friends with the female protagonist because of how he feels towards Chidori. During some point of his social link, Junpei found out someone was taking candid photos of the female protagonist, and he subsequently helps her find the culprit. When his S.Link is maxed, Junpei will give the female protagonist a pig key holder, an item he used to keep his house keys. Since he moved to the dorm, he had kept his house keys with him, due to the circumstances involving his father.

Junpei returns as a playable character in Persona 4 Arena Ultimax. He is the coach of the little league and one of the Shadow Operatives Auxiliary Team (reserve team). After giving a good speech and advise to the team despite they lost, he dozed off in the train, tired. He was then daydreaming that he won the WBC (World Baseball Championship) for his team and proposed to Chidori...only to be waken up by the conductor at Inaba Station, telling him this is the last stop. Coincidentally, Yukari calls him and she was surprise that he's in the location where her, Ken, Koromaru, Labrys and Kikuno are headed and tells him to wait for them at the station but his phone's batteries dies. He decides to head to the convenience store, thinking that it's a good place to charge his phone and get a snack. But his luck went worse when the red fog appears and he has to fight S.Yukari and being mocked by General Teddie for being a yapping idiot and also a mook when he wins. Soon he decides to find his friends and end up with some misadventures.

Junpei's leitmotif is called "Mr. Easy-Going Man". The console version of the theme features more rock/guitar instrumentals compared to the original arcade version.

Junpei is a hard-hitting character with the capability to use Trismegistus to set up for several wall bounce combos. Swapping out his two-handed sword for a bat, Junpei's moves are more baseball-based and have the ability to reflect certain projectiles with a precisely timed swing. He can also summon Trismegistus overhead and use fire moves to control the distance between him and the enemy. However, while he does have multiple tactical options, he can be limited by his average attributes.

Junpei's battle style is greatly influenced by the baseball scorecard right next to his SP Gauge; understanding how to use this is key to Junpei's gameplan. Every time Junpei manages to hit his opponent with his bat, he gets a single, or a runner on a base. In the same way, reflecting projectiles with the bat counts as a single as well. This continues until he gets a runner on all bases, after which hits get a runner back to home base, thus scoring a run and adding another point to his scorecard. Each run scored progressively gives Junpei the capacity to deal more damage per hit. In addition, the number of runs he scores is kept between rounds. Once the scorecard reads 10 runs, he automatically activates his install, Victory Cry, when his current combo ends which, upon activation, will stay with him until the end of the match. Victory Cry, other than giving him an overall boost and slowly regenerating his HP (not unlike Spring of Life), will make bat hits as Clean Hits which will increase untechable time, which gives Junpei more room to perform combos.

While this should mean that after 13 hits have been made with the bat, Junpei is at maximum power, there are other factors to consider. When Junpei gets tagged with an attack or a combo, he receives an out, with three outs clearing the runners from their bases, forcing Junpei to fill the field again to continue scoring points. In addition when Junpei whiffs his bat, he gets a strike, with three strikes resulting an out. But when Junpei's bat gets blocked, Junpei gets a ball with 4 balls giving him a runner on base. When using his Supers, Junpei is able to allow the runners to all score points, after which he himself scores a home run. Thus at the price of his runners at their bases, Junpei can further advance toward his quota.

Junpei shares the same Japanese voice actor, Kōsuke Toriumi, with Eikichi Mishina from the Persona 2 duology. Both characters share some similar personality traits, such as a rivalry with a female character who has feelings for the main character and a clear love interest.

Junpei's level up quote, "ta da da da!", is originally "teretettē" (テレッテッテー) in the Japanese version. The sound and rhyme likely allude to the viral jingle of the Fist of the North Star series, otherwise commonly translated to onomatopoeia as "tērettē" (テーレッテー).

This eventually becomes an ascended reference, especially in Japanese by the announcer in The Ultimax Ultra Suplex Hold.

The Shirt of Chivalry, a type of costume for males in FES and P3P, is noted for the kanji symbols on their backs that symbolizes the character themselves. Junpei's kanji means "Color" (色), as in his colorful personality. The kanji also means "dirty minded", "sexual desire" or "variety", a trait of Junpei used for humorous purposes.

Orignally in Persona 3 Portable there is a "good" ending of female protagonist with Junpei confessing his love for her like the other male teammates. This was scrapped from the finalized version but the data remains in the game disc and Junpei's Japanese voice casting for this ending can be heard.

If one hacks Persona 4, Junpei's character model can be found. This is almost certainly because Persona 4 was built on the Persona 3 engine, resulting in many leftovers including Japanese voice clips, music tracks, and portraits.

During his Persona summoning Junpei may say "I can't lose to him," referring to the male protagonist. He still says "him" in the female protagonist's route.

In the anime Persona -trinity soul-, someone resembling Junpei appears as a brief cameo in episode 13 when Ryou Kanzato is looking around as he is leaving the police department.

In Persona 4 Golden, if Yosuke Hanamura has the Gekkou Uniform equipped, he will mimic Junpei's victory pose after battles, as well as say Junpei's lines. Befitting since they are both of the Magician Arcana.

Junpei is the only Persona 3 character to summon Persona without using Evoker in other moves in Persona 4 Arena Ultimax. Akihiko can be sometimes counted while not using his Awakening Super and Instant Kill.

Junpei is unique among Persona-users of the Magician Arcana, in that his two Persona are heavily physical based in an arcana known more for magical ability.

Ultimax reveals that Junpei is a fan of Rise Kujikawa. He's excited to fight her in his intro pose, and he has a special win quote if he wins against her.

In Ultimax, Junpei's Clean Hit mechanic is actually pre-dated by Guilty Gear character Sol Badguy (as the introduction of the mechanic was introduced in Guilty Gear XX Slash-onwards).

The theme of the clean hit also befits Junpei's baseball theme as well, as a clean hit is a term used for baseball, and in other fighting games that share this rare mechanic, it is described mainly as a type of hit landed directly at the central point of the target at the right positioning.

Answering a fan question for the Persona Stalker Club show, Atlus said that the necklace Junpei wears during Persona 4 Arena Ultimax is from Chidori's favorite apparel brand, which she gave to him as a gift.